Carburetor



R. F. BRACKE Dec. 5, 1939.

CARBURETOR Filed Jan. 16, 1956 4 Sheets-Sheet l 4 Sheets-Sheet 2 R. F. BRACKE CARBURETOR Filed Jan. 16. 1936 Dec. 5, 1939.

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' ez IM R. F. BRACKE Dec. 5, 1939.

GARBURETOR Filed Jan. 16, 1936 4 Sheets-Shes?I .'5

Patented Dec. 5, 1939 UNITED STATES PATENT OFFICE cAnBURETon Robert F. Bracke, Chicago, Ill.

Application January 16, 1936, Serial No. 59,327

18 Claims. (Cl. 12S-119) My invention pertains to carburetors and is more particularly concerned with carburetors of the self-feeding type which are especially adapted for use on automotive vehicles.

5 An object of my invention is to provide an improved carburetor which affords maximum power and acceleration with economical fuel consumption.

Another object is to provide a carburetor having l improved means for adjusting and controlling the richness of the combustible mixture supplied to the engine.

Another object is to provide a carburetor having an improved air valve and control therefor,

l whereby varying needs of the engine for diierent conditions of operation are satised more elciently.

vAnother object is to provide a carburetor having improved means for facilitating starting of a cold engine.

Another object is to provide a carburetor having improved means for facilitating starting of a hot engine. l

Another object is to provide a highly efficient carburetor which will be economical to manufacture and which will aord trouble-free service. Another object is to provide a carburetor which will free itself of any oil carried into the carburetor from an air strainer and cleaner.

Another object is to provide a carburetor having an improved ioat for better withstanding the suction maintained in the fuel chamber, l

`Other objects and advantages will become apparent as the description proceeds.

In the drawings,

Figure 1 is a diagrammatic sectional view of one form of carburetor. embodying my invention;

Figure 2 is a vertical section taken on the line 2 2 of Figure 3;

Figure 3 is a vertical section taken on the line 3 3 of Figure 2;

Figure 4 is a horizontal section taken on the carburetor in which the only differences reside in a the air cleaner for the air valve control chamber and the relief means" for the accelerator pump, and wherein Figure 8 is a section taken-on .the line 8 8 of Figure 10; I'

Figure 9 is a vertical section taken mainly on the line 9 8 of Figure 10 but wherein the lower 5 part showing the throttle valve is taken on the line 9' of Figure 10; and

Figure 10 is a horizontal section taken on the line I0 I8 of Figure 9.

Referring to the drawings, I have shown my 10 carburetor as composed of three main castings, an upper casting A, a center casting B, and a lower casting C. These castings may be secured together by any suitable means such as the screws I2, and a gasket I4 is preferably interposed be- 15 tween the center and lower castings. In the present state of the art, carburetors used in large quantities are most economically manufactured by the die casting process of zinc base alloys and, while the castings A, B and C may be made of any 20 suitable material and by any desired process, IA have designed them so they -may be easily and economically manufactured by the usual die casting process.

The carburetors shown in the drawings are of 25 the dual jet type and are provided with a pair of nozzles or fuel-feeding Venturi tubes I6 and I8. Each nozzle discharges into a mixing chamber 20 or 22, the upper or inlet end of each mixing chamber is dened by a secondary Venturi 30 tube 24 vor 26. These secondary- Venturi tubes are preferably made as separate rings which are press-fitted or otherwise secured in place, as indicated most clearly in Figure 8.

Each nozzle is in the form of a primary Venturi 35' tube and is thradedly secured in the central casting B, as best indicated in Figure 2 of, the draw V ings. The lower or discharge end of each nozzle is located a short distance below the throat of its corresponding secondary Venturi tube 24 or 26 40 so that each nozzle discharges into its mixing chamber at the point of maximum suction in thatv` mixing chamber. This affords maximum eiliciency of operation for'the nozzles I6 and I8.

Mixing chambers 20 and 22 communicate with 45 throttle bores 28 and 30, respectively, and each throttle bore in turn communicates with a section of aninlet manifold. My carburetor is particulariy designed for use with multi-cylinder engines wherein each section of an inlet manifold supplies combustible mixture to a plurality of cylinders.

A pair of throttle valves 32 and 84 are provided, these throttle valves comprising disks of relatively thin material mounted on a common shaft 36 provided at one end with a lever Il adapted to be connected in the usual manner with the i controlled by an automaticair valve 42. vThis air 4 hand control of an automobile or other vehicle. Secondary air for intermixture with the relatively rich mixtures provided by the nozzles l0 and i8 is admitted through a common inlet 40 valve comprises a disk 44 of sheet material carried by a shaft 40 having reduced ends or journais 48 and 50 pivoted in bearing caps 52 and 04,' respectively, which are screwed into opposite sides of the central casting B. The reduced size ofthe journals 48 and 50 is of great importance in reducing the frictional resistance to rotation of the airvalve 42 and results in an air vvalve which is extremely sensitive and which accurately apportions the secondary air according to the varying needs oi.' the engine.

The means for opening and Aclosing the air valve 42 is shown diagrammatically in Figure l and in detail in Figure 9. This means comprises an arm 5,6 which is attached to the air valve shaft 4t by means of a set screw 58. Thet other end ofthe arm 5B is drilled to receive the bent-over upper end of a piston rod 6E! whose lower end is connected by means of a universal connection to a piston 62. The piston @2 reciprocates in a cylinder @e provided by a sleeve G6 of brass or other suitable material which is press-fitted into the central die casting B in order to reduce the frictional resistance to movement of the piston 5.2. The piston S2 is urgedupwardly by a spring Su, and the upper position of the piston"62 is determined by the engagement of the end of the lever 0S with the upper wall 'it of a chamber i2 located above the cylinder Sli. l

Theparts are so constructed and arranged that when the arm 56 engages the wall lil the secondary air valve 42 is slightly open, that is, the

right and left-hand edges of the valve, as viewed in'Figure 8, do not engage the wall of the passage in which the valve is located. This is important .throats of secondary Venturi tubes 24 and 28 in as it facilitates ease of operation of the valve and prevents the wedging action which would occur between the edges of the valve and the wall of its passage if the valve were permitted to close completely. This feature, in combination with the small bearings on which the lvalve pivots, pro duces an extremely sensitive and eillcient valve.

The cylinder 64 is in communication with the j the manner hereinafter described, and the suction created in the throats of these Venturi tubes extends to the cylinder 64 and tends to draw the piston 62 downwardly, thereby opening the valve 42. 'Ihe degree of suction created in the throats closed, in accordancewith the needs of 24 land 20. As shown most clearly in Figures 1 and 8, these secondary Venturi tubes have their throats provided with steps 12 and 14, respectively, and below 'the' steps are the series of radial openings 10 and 10, each series -communicating with an annular groove 00 or l2.

.As shown most clearly in mme s, these sbclondary Venturi tubes are' formed as separate sleeves which are press-fitted into the central and lo'wer castings of the carburetor. A slot 04 (Figures l and stormed in the wall of the central, casting, establishes communication between the annular grooves 00 and 82 of the two secondary Venturitubes.

The cylinder 64 communicates with these annulargrooves through vertical duct 06 and horizontal duct 88. A plug 90 is press-fitted into the vertical duct 86 and carries a metering orifice for accurately controlling the communication between the cylinder 04 and the throats of the secondary Venturi tubes. l

It is necessary that the chamber 12, located above the piston 62, be in communication with atmosphere, but it is also important that no dirt be permitted to enter this chamber and interfere with the operation of the piston 62. I accordingly provide means to illter any air which is admitted to the chamber 12, and in the drawings I have illustrated two forms of iilteringI means.

In the embodiment of Figures 1 to 7, inclusive, I have shown the chamber 'l2 as being in coimmunication with one end bore of a series of spaced bores 92 formed in the upper casting A. These bores 92 overlap a complementary series of bores 94 formed in the upper end oi the central casting B. The end bore of the lower series Q6, which is remote from the chamber l2, cornfinunicates with atmosphere through an opening l98.

'The purpose of this structure is to provide a relatively long pathway for the air entering the chamber 12, this pathway being provided with a series of sharp turns iorseparating the air from "any dust contained therein. This winding pathway-also provides a series of pockets in which the dirt removed from the air may collect. This form of air cleaner has proved to be very eiilcient in service.

In the embodiment shown in Figures 8 to l0, inclusive, the chamber l2 receives' its air supply through `a ltering chamber in which maybe- Y located any suitable and conventional iiller for removing the dirt from the air. More specifically, the chamber 12 is in communication with one end of a passage |00 leading to an arcuate chamber |02 -formed partly in the upper casting and partly in the central casting. The other end of this chamber |02 communicates with atmosphere through an opening |04. In vthe chamber |02 I place any suitable air ltering media |00, such as a mass of metal shavings, textile fibers, etc. I have found that when the engine is operating with wide open throttle, it is desirable -to provide some means in addition to the piston 0 2 and cylinder 64 for holding the air valve 42 in fully open position. I accordingly mount a vane |00 on the upper side of the air valve 42 and in such position that as the air valve opens the inrushing. f

air impinges upon this vanef'and tends to increase the opening of the air valve. This vane is made of such size that it has no appreciable etlect l upon the opening of the valve 42 except when the engine is operating under substantially full throttle and at substantially top speed.

Just below the shaft 40 of the air valve 42 I provide a vertical baille |00 which eliminates the eddy currents which might otherwise be formed by the .inrushing air in the space immediately beneath this air valve.

I shall now describe the means for supplying `fuel to the nozzles l0 and il from the' carburetor ||2 and lll. At thelmper ends 0f these cylinders are plugs ||0 and lil press-utted into the central casting B. These plugs carry accurately metered orices in which are located economizer pins |20 and |22, respectively. Above these plugs II6 and II8 are chambers I24'and |26 closed at their upper ends by removable caps I28 and |30.

The chamber |24 communicates with the nozzle I8 by way of passage |32, annular groove |34, and diagonal passages |36 which open into the throat of the nozzle I8 just below the step therein. Chamber |26 similarly communicates with nozzle I6 by way of passage I38,.annu1ar groove I40and diagonal passages |42 which open into the throat of the nozzle I6 just below the step therein.

The fuel thus supplied to the nozzles I6 and I8 mixes with the air owing through these nozzles, and the mixtures thus formed are discharged into the respective mixing chambers with which the nozzles are associated. Each nozzle receives its supply of air through an inlet |44 provided by the upper casting A. I utilize the economizer pins |20 and |22 to regulate the richness of mixtures supplied by the nozzles I6 and I8 in a man-- ner'which I shall now describe.

The economizer pins |20 and |22 are carried, respectively, by pistons |46 and |48. These pistons are urged downwardly by springs |50 and |52 and are raised. by piston rods |54 and |56. It is to be noted, as shown most clearly in Figure 3, that the pistons reciprocate in cylinders provided by the central casting B, whereas the piston rods |54 and |56 reciprocate in guides |58 and which are threadedly engaged in the lower casting C. It is undesirable to increase manufacturing costs by requiring accurate align-v ment between the guides |58 and |60 and the cylinders I|2 and ||4 and, in order to make such accurate alignment unnecessary, the upper ends of the piston rods |54 and |56' are slightly rounded and engage fiat surfaces on the lower sides of the pistons |46 and |48.

The lower ends of the piston rods |54 and '|56 rest upon case-hardened steel disks |62 and |64 which are riveted, respectively, to brass sleeves |66 and |68 adjustably threaded in one end of a common lever arm |10. The sleeves |66 and |68 have heads |12 and |14 provided with longitudinal grooves for engagement by spring-pressed detents |16 to hold them ir adjusted position.

oted in the lower casting C and carrying a second arm |80 attached by means of link |82 to the lever |84 which oscillates the throttle valve shaft 36. -The lever |84 is provided with the usual ,|82 ofr materially less diameter than the head.

' The economizer pins may be individually adjusted by means of the brass sleeves |66 and |68. f

In the idling position of the throttle '.valve the adjustment of the economizer pins is such that the tapered portions |80 are located in the orifices of the plugs |I6 and II8 to greatly restrict the iiow of fuel to `thenozzles I6 and I8. As the throttle valves are opened, the economizer lpins y vious embodiment.

I move upwardly through the orifices in the plugs I|.6 and |I8 so that a small opening 'of the vthrottle valves will bring the cylindrical por- .pins are located' in the metering orifices of the plugs I|6 and ||8 and afford no appreciable restriction to the'flow of fuel to the nozzles I6 and I8. In this manner the carburetor is permitted to develop 4full engine power while the mixture supplied by the nozzles I6 and |8 is graduated in accordance with the needs of the engine to afford maximum economy of operation.

The pistons |46 and |48 and` cylinders ||2 and I |4 comprise -parts of accelerator pumps for supplying additionalfuel to the nozzles I6 and I8 during periods of acceleration. 'I'l'ie pistons |46 and |48 are provided with ports 200 and 202 through which the fuel normally passes to the nozzles I6 and I8. Above these ports are yvalve disks 204.and 206 which are raised from theirseats by suction to permit fuel to flow through the ports 200 and 202 during normal engine operation. Each of these 'valve disks 204 and 206 may be provided with a small orifice capable 'of supplying sufficient fuel when the engine is idling so that during idling operation these valves may remain upon their seats.

When the throttle valves are suddenly opened through a wide range, the accelerator pumps would supply too much fuel to the nozzles I6 and I8 unless some relief means were provided. In Figures 1 and 2, this relief means takes the form of a spring-pressed relief valve 208 controlling the outlet of a chamber 2I0 which communicates through port 2| 2`with the upper ends of both of the accelerator pump cylinders ||2 and II4. When the throttle valve is suddenly opened through a wide range, the pressure developed on the fuel by the accelerator pump pistons causes the valve 208 to open against the tension of its spring 2| 4 which permits fuel to return to the i bottom of the fuel chamber by way of the pas- 'I'he arm |10 is mounted on a shaft |18 pivsage 2I6.

In the embodiment of Figures 8, 9 and 10, a different means is provided to prevent oversupply of fuel to the nozzles bylthe accelerator pumps. In this embodiment the chamber 2I8 corresponds tothe valve chamber 2|0 of the pre-I `This chamber 2I8 communicates with a vertical return passage 220 and at the lower end of this return passage there are two pairs of bores 222, each pair leading back into oneA of the accelerator pump cylinders. The two sets of bores 222 are staggered, as indicated in Figure 9, and are so located with respect to the accelerator pump cylinders that when the accelerator pump pistons are in their lower or normal positions these pistons close theoutlet ends of these bores.- As the pistons rise during the opening movement of the throttle valves, they successively uncover the discharge ends of the bores 222 to permit increasingly free return flow of fuel from the upper ends of the accelerator pump cylinders to the fuel chamber.

The float chamber |08 is supplied withV fuel from the vmain fuel supply'tank. Interposed between the float chamber |08 and the main fuel tankis a st Liner chamberv 224 having an inlet 228 connected by piping to the main'fuel supply tank. The fuel entering the inlet 228 passes into the chamber 224 on the outside of a screen 228 attached to rings 238 and 232 surrounding a central tube 234 carried by a removable head 238. By removing the head 238, the entire assembly, including the tube 234, rings 238 and 232, and screen 228, may be removed as a unit to facilitate inspection and cleaning of the screen 228. The fuel passing through the screen 228 flows through the openings in the tube 234' and upwardly through this tube and into passageway 238 leading to the iioat chamber |88.

'I'he inlet valve 240 controls the admissionof fuel to theA float chamber |88 fromthis passage 1 238. This valve is opened by gravity andis closed buretor. Some means must therefore be provided to raise the fuel from the main fuel tank to the engine carburetor. This means will next be described.

The upper casting is shown in Figure 10 as being provided with three bores 248 leading to a manifold'248 communicating with the upper end of a passage 250 (Figure 8). The lower end of l'. the passage 258 communicates with a horizontal duct 252 which terminates at a choke plate 254'.

l As shown most clearly in Figures 5, 6 and 7, this choke plate carries a hollow cap 258 Awhich is divided into two chambers by a central partition- 258. The cap 258 is pressed against the plate 254 by a spring 288 beneath the head of a bolt 282 which secures the plate 254 and cap 258 to a laterally extending boss of the central casting.

- Plate 254 has a port 284 (Figure 5) which normally registers with the end of the passage 252 to admit air to the chamber 288 of the cap 258. 'I'he choke plate- 254 has asecond and generally pear-shaped opening 288 which normally connects the chamber 288 with the inlet end of a booster Venturi tube 218. In the position of the parts shown in Figure 5, air is admitted to the inlet end of the booster 218 and passes through this booster to discharge into 'a space 212 (Figure 9). This space connects with a chamber 214 which communicates with one of the mixing chambers through a port 216. The chamber 214 also communicates with the air inlet immediately above the secondary Venturi tubes through a passage 218.

Between the space 212 and chamber.214 is a metal disk 288 carrying a metered o` ce 28| through which passes the tapered lower nd of a pin 282 attached to the 'air valveipiston 82.

'Ihe suction existing in the mixing chamber 28 is communicated in lessened degree through passage 218, chamber 214, orifice 28|' and space 212,'

to the booster 218 to cause air ow therethrough. The throat of the booster 18 has a slight step Just beyond which are radial passages 282 communicating with bores 284,and 288 leading to the top of the float chamber |88 for the `purpose of creating suicient suction therein to lift fuel from the main fuel supply tank to this chamber.' As the fuel needs of the engine increase with the opening of the throttle valves, greater quantities This float is a hollow metal shell aiaasso of fuel must be drawn from the main fuel tank to the float chamber, and it is desirable under these conditions to permit the degree of suction existing in the float chamber to increase somewhat with the opening oi 'the throttle valve: However, unless some means were provided to regulate this increase, the arrangement so fardescribed would provide more increase in fuel chamber suction than is desirable.

The means for regulating the fuel chamber suction for diiferent conditions of engine operationcomprises the tapered lower end of the pin 288 which is located in the metered orifice 2,8 I. This pin is carried by the piston 82 in suchmanner that as the secondary air valvel opens the tapered end of the pin 288 moves downwardly in the orince 28| and increasingly reduces the effective'size thereof. It will, of course, be appreciated that the taperedend of this pin can be shaped to give any desired rate oi' increase ofv fuel cham. ber suction.

The greater degree of suction in the fuel chamber, the less the head available to raise fuel from the float chamber to the nozzles |8 and I8. In

order, therefore, to improve the acceleratingcharacteristics of the engine, I find it desirable to retard the increase in float chamber suction dur-v ing the accelerating period.' This I accomplish by interposing a restriction 288 in the passage 288 which connects the throat of the booster 218 with the float chamber |88. This restriction is in the form of a separate piece having a metered orifice, this separate piece being press-fitted into the passageway 288.

My carburetor is designed for use with air cleaners and silencers of the types now commonly used, and I contemplate that the upper part of my carburetor will be attached to an air cleaner and silencer in such a manner that all of the air entering the carburetor through the openings, |44 and 248 will have been cleaned of dirt' by such means before reaching the carburetor. Some of these cleaners contain quantities of oil, and I have found it desirable to providey special means for preventing this oil from interfering with the operation of the carburetor. The booster and the air valve control mechanism are `the only parts of the carburetor which might be undesirably affected by the presence of this oil in any air supplied thereto. I have alreadydescribed the means for cleansing the air supplied to lthe chamber 12 of the air valve control mechanism, and I shall now describe `'the means for preventing this oil from interfering with the operation of the booster.

The vertical passage 258, which supplies the booster 218 through the cross passage 252, continues downwardly below this cross passage and opens into a conduit 232 which communicates with the chamber 214 through a 4diagonal duct 284. Any oil which may be contained in the air admitted through the booster inlets 248 will continue downwardly past the passage 252 leading to Iy have found it desirable toy provide 'meansifor -preventing any leakage of air into thejiloato chamber around -the piston .rods |54,a.ridv |58. To accomplish lthis I provide the'guides| 58 angl |88 with radial bores 388 and-382- connecting with diagonal ducts 384 and '388'1eading to a conduit 388 whichiempties into both` throttlebores 28 and 30 through an interconnecting open-- ing 3|0. The conduit 308 has a branch 3|2 leading to the mixing chamber 22 above the throttle valve 34, and a. plug 3|4 is press-fitted into the:

lower end of the conduit 308 to restrict flow therethrough. In this manner intermediate portions of the piston rods |54 and |56 are exposedv I have provided special means associated with.

the choke late 254 for facilitating starting of the engine when cold. This choke plate 254 has an arm terminating in a knob 3|6 adapted to be connectedto the usual hand choke control on the instrument board of an automobile, whereby this choke plate 254 may be shifted .from the running position, shown in Figure 5, to the fully choked position, shown in Figure 6, or to any intermediate position.

As thechoke plate 254 is moved from the position of Figure 5, toward the position of Figure 6, the pear-shaped orifice 268 restricts the flow of air into the booster 210, thereby reducing the degree of suction which this booster maintains in the float chamber |08 and thus permitting the nozzles |6 and I8 to draw more fuel from this float chamber and provide richer mixtures. When the choke plate 254 is moved to fully choked position, the air supply to the booster 210 is Aentirely cut off, as shown in Figure 6.

As the choke plateI 254 is moved to choked position, a comet-shaped opening 3|8 registers with one end of a passage 320 opening into the air valve control cylinder 64, thereby reducing the degree of suction created therein and which is available for opening the air valve 42. When the choke plate 254 is in fully choked position,

free communication for air isestablished between the air inlet 246 and the cylinder. 64, whereby substantially atmospheric pressure is maintained in this cylinder and the secondary air valve 42 remains closed.

It will be understood that the capl 256 rotates with the choke plate 254, the plate being provided with a pin 322 extending into ahole provided in the cap to insure this relationship. Movements of the choke plate 254 are limited by the engagement of stops 324 and 326 with a stationary pin 328.

As the choke plate 254 and cap 256 are moved toward choked position, an arcuate slot 330 in the plate 254 establishes communication between a bore 332 opening into the space beneath the air valve 42 and a bypass passage 334 communicating with the throttle bore 30 at 338. The opening of this bypass between the space beneath the air valve 42 and the throttle bore 30 has substantially the same effect as opening` the throttle valve slightly and thus facilitates start' ing of the engine.

It is frequently difficult to start a hot engine due to the fact that the mixture supplied to the engine under these conditions is richer than necessary. A feature of my invention lies in the provision of means to overcome this difficulty and to make the starting of an engine which is extremely hot as easy to accomplish as the starting of an engine at normal operating temperature. 4

The means for carrying out this feature of my invention is best shown in Figures 1 and 9 of the drawings. In these figures I have shown the throttle bore 28 as provided with an opening 340 which is shown as closed by a valve 342 carried on the lower end of a bimetallic strip 344 having its upper end bent outwardly and attached to the central casting by a bolt 346 which also carries a protecting shield 348. The parts are so constructed and arranged that when the engine is stopped while it is extremely hot the heat of the engine causes the bimetallic thermostatic strip 344 to flex in such a way as to move the valve 342 away from the end of the opening 340, the outward movement of this valve being limited by the shield 348. If an attempt is made to start the enginewhile still inthis extremely hot condition, air will be drawn through opening 340 into .throttle bore 28, thereby reducing the richness of the mixture supplied to the cylinders connected with that section of the manifold connected to the throttle bore 28.

My carburetor has been used in connection with a V type eight-cylinder engine wherein each manifold section supplies four cylinders, and this hot starting feature of my carburetor has proved to be very eective in this installation. It will be noted that the throttle bore 30 and section of the manifold connected therewith is not appreciably affected by the opening of the valve 342 so that the cylinders supplied from the throttle bore 30 receive the normal starting mixture which will be available for starting the engine in the event that too lean a mixture is creat-ed in the throttle bore 28 by opening of the valve 342. As soon as the engine starts, the suction created in the throttle bore 28 is sufficient to close the valve 342 against the resistance of the bimetallic strip 344. This means that, no matter how hot the engine may become while it is operating, the valve 342 will always remain closed until the engine stops.

The operation of my invention is as follows:

When the engine is operating with the throttle valves 32 and 34 partly open, air is admitted to 4the nozzles |6 and |8 through inlet |44, and the air passing through the restricted throats of these nozzles draws fuel from the oat chamber |08. The mixture thus formed is delivered into the mixing chambers 20 and 22 at substantialll7 the points of maximum suction therein, and mixes with air admitted through the inlet 40 and past the partially opened secondary air valve 42.I

The suction created in the throats of the secondary Venturi tubes 24 and 26 is exerted on the air valve control piston 62 and pulls this piston downwardly against the tension of the spring 18 to maintain the air valve 42 in partially open position. 1

Air ls also admitted through inlets 246 and passes through booster 210 and is discharged into mixing chamber 20. The ow of this air through the throat of the booster 210 creates suction therein which is communicated to the upper end of the float chamber |08 and is effective to draw fuel from the main supply tank to this float chamber through the filter screen 228.

When the throttle valves are opened to accelerate the engine, the accelerator` pump pistons |46 and |48 are raised in their respective cylinders and the valves associated with the4 tops of these pistons are closed, thereby forcing fuel to the inlets I6 and |8. If the throttle valves are opened through a wide range the pressure produced by the pistons |46 and |48 will result in opening of the relief valve 208 which permits part of the fuel supplied by the accelerator pumps to return to the fuel chamber through bypass -conduit ZIB. A

As the fuel needs of the engine change with different positions of the throttle valves, the economizer pins |20 and |22 shift their positions with respect to the orifices in the plugs H6 and ||8 to regulate economically the degree of richness of the mixture supplied by the nozzles I6 and I8. The increased suction created in the throats of the secondary Venturi tubes 24 and 26, as a result of increased opening of the throttle valves, is communicated to the secondary air valve control cylinder 64 and moves the piston 62 downwardly therein to further open the secondary air valve 42. This downward movement of the piston 62 lowers the tapered end of the pin` 288 further into the orice 28| to prevent undue increase in iiow through the booster 210. The small amount of increased flow which occurs through the booster, as a result of opening of the throttle valves, is prevented by the restriction290 from immediately affecting the float chamber suction, and in this manner the acceleration of the engine is further improved.

When the throttle valves are substantially wide open and the engine is operating at substantially its maximum speed, the flow of air past the secondary air valve 42 impinges on the vane |96 and assists in the complete opening of this yalve. During the periods when the engine is operating at or vnear full throttle, the economizer pins |20 and |22 offer no restriction to the ow of fuel to the nozzles I6 and I8.

In starting a cold engine, the choke plate 254 is shifted to restrict or entirely cut off the now of air through the booster 210, thus reducing the degree of suction existing in the float chamber |08 and permitting the nozzles I6 and |8 to draw more fuel therefrom and to supply richer mixtures. At the same time air is admitted to the secondary air valve control cylinder 64 to prevent the creation of any suction therein, with the result that the secondary air valve remains closed. This movement of the choke plate also creates a bypass around the throttle valves to increase the supply of combustible mixture to the engine cylinders.

If the engine isstopped while it is extremely hot, the bimetallic strip 344 opens the valve 342 to establish communication between one throttle bore and atmosphere. If the engine is started while in this extremely hot condition, air is drawn in through the opening 340 and the richness of the mixture supplied to one-half of the engine cylinders is reduced. 'This greatly improves the starting characteristics of these cylinders under these conditions. As soonv as the engine starts,

the valve 342 is drawn shut by the suction created in the associated throttle bore, and this valve remains shut during engine operation, regardless of engine temperature.

It is to be understood that my invention is not limited to the specific details shown in the drawings and described in the specification, but that my invention may assume variousforms and that 1 the scope of my invention is to be limited solely by the following claims.

1. In a carburetor of the class described. the combination of a pair of fuel feeding nozzles, a separate mixing chamber for each nozzle, a secondary Venturi tube defining the inlet to each mixing chamber, a common inlet for secondary air, a valve controlling said last-named inlet, and means for shifting the position .of said valve in accordance with the .mean of the variations in suction occurring at the throats of said secondary Venturi tubes.

2. In a carburetor of the class described, the combination of a fuel feeding nozzle, a mixing chamber into which said nozzle delivers, a secondary Venturi tube through which secondary air is admitted to said mixing chamber. a valve for controlling the admission of secondary air to said mixing chamber, suction operated means connected with the throat of said secondary Venturi l0 4 accordance with suction variations in a part of said carburetor, and a vane carried by said valve and adapted to be impinged upon by air passing therethrough for assisting said suction actuated means in holding said valve in fully open position during maximum speed of operation of an engine to which said carburetor is attached.

4. In a carburetor of the class described, the combination of a fuel feeding nozzle, a fuel chamber from which said nozzle is supplied, a booster Venturi tube for creating a suction in said fuel chamber, means for varying flow through said booster to vary the suction created thereby, and means for delaying the effect on said fuel chamber of variations in suction produced by said booster.

5. In a carburetor of the class described. the

combination of a fuel feeding nozzle, a fuel chamber from which said nozzle is supplied with fuel, a booster for creating suction in said fuel chamber, an accelerator pump for supplying additional fuel to said nozzle, a piston rod for operating said pump, a throttle valve, a connection between said throttle valve and piston rod, said connection including an adjustable brass sleeve carrying a case-hardened disk engaging said piston rod, guide means for said piston rod, a suction connection between an intermediate portion of said guide means and opposite sides of said throttle valve, and a. restriction in said connection limiting' bypassing of said throttle valve therethrough.

6. In a carburetor of the class described, the combination of a pair of fuel feeding nozzles, a pair of accelerator pumps for supplying additional fuel to said nozzles during acceleration, and common relief means for both of said pumps.

7. In a carburetor of the class described, the combination of a pair of fuel feeding nozzles, a pair of accelerator pumps for supplying additional fuel to said nozzles during acceleration, leach pump comprising a cylinder having a piston reciprocable therein, relief means including a bypass passageway, `and openings leading from saidpassageway into said cylinders arranged to be succossively uncovered by said pistons to permit relief flow of fuel therethrough.

8. In a' carburetor of the class described, the combinationof a fuel' feeding nozzle,- a source of fuel supply for said nozzle, a conduit leading from said nozzle to an intake manifold of an engine, an atmospheric opening for said conduit, a valve for closing said opening, and thermostatic meansfor openingV said valve when said engine is extremely hot and is not operating, safd means being unable to maintain said valve in open poslf tion againstthe closing force of suction created in said conduit when the engine is operating.

9. In a carburetor ofthe class described, thev a bimetallic strip tending to open said valve when said engine is extremely hot, the opening force of said strip being insuicient to overcome suction created in said throttle bore during engine operation, and means for limiting the opening movement of said valve.

10. In a carburetor of the class described, the combination of fuel `feeding means, a pair "of throttle bores, each throttle bore communicating with a part of an intake manifold of an engine, an atmospheric opening in one bore only, and a thermostatic valve controlling said opening to ad' mit air therethroughonly when the engine is hot and not operating.

l1. In a carburetor of the class described, the combination of a fuel feeding nozzle, a oat chamber from 'which said nozzle is supplied with fuel, a booster for creating suction in said oat chamber, an air inlet conduit for said booster, said inlet conduit being adapted for connection to an air cleaner containing oil, and means for preventing oil from being carried into said booster by air entering `through said inlet. conduit, said means comprising an extension of said air inlet conduit to a point below said booster, and a connection between the lower end of said conduit and a part of said carburetor subject to suction.

12. In a carburetor of the class described, the' chamber into which said nozzle delivers. a fuel .chamber from which said nozzle is supplied with mixtures delivered bysaid-nozzle. y A

14.. a carbureator of the class described, the

fuel, a booster for creating suction in said fuel chamber, a secondary air valve for controlling admission of air to said mixing chamber, a vacuum cylinder regulating said airvalve, a throttle valve between said mixing chamber and an inlet manifold of an engine, and means for facilitating starting of a cold engine, -said means including a movable cup having a pair of chambers, one chamber being shiftable to reduce the suction created by said booster and to reduce the effectiveness of said vacuum cylinder, andthe other .f

chamber being shiftable to bypass said throttle, and means for shifting said cup.

13. In a carburetor of the class described, the combination of a nozzle feeding a mixturev of fuel and air, 'i-mixing chamber in to which said nozzle discharges, a secondary air inlet for said mixing chamber, a valve automatically controlling said inlet, manually operated means to facilitate starting a cold engine Aby increasing the richnessand quantity of mixtures delivered by said nozzle and maintaining said valve in closed Y position, and automatically operated means to facilitate start- -ing a hot engine by reducingthe richness of combination of a pair of nozzles feeding mixtures of fuel and air,`a throttle valve interposed` ble,-Y tween each nozzle and a section of ar. inlet manifold of an engine, means to facilitate starting a cold `engine by increasing the richness and quan-v .Y

tity of mixture delivered by both of said nozzles.

and means to facilitate starting a hot engine by reducing the quantity ofmixture delivered by one of Ysaid nozzles only.

15.'In a carburetor of the class described,.the`

combination of a die cast body, a nozzle feeding a mixture of fuel and air, a mixing chamber into which said nozzle delivers, an air valvefor admitting secondary air to said mixing chamber, said air valve comprising a disk of thin materialJ a central pivot for said disk whereby said valve is balanced with respect to air admitted therepast,'a suction cylinder comprising a brass sleeve carried in said body, a piston reciprocable insaid sleeve, a connection between said piston and said valve, a spring for moving said piston in a direc-.` tion toclose said valve, means for admitting,-

suction to said cylinder to move said piston in the opposite direction, a stop for preventingcomplete closing of said valve, substantially friction- I less bearings for said valve, a vane carried by said yvalve to increase the opening in saidvvalve under certain conditions of engine operation, and a baille located beneath said valve to prevent the formation of whirling currents in the air passing said valve.

16. In a carburetor of the class described, the combination of a pair of fuel feeding nozzles, a float chamber from which said nozzles are suppliedwith fuel, a mixing chamber into which each nozzle delivers, a secondary .Venturi tube at the inlet of each mixing chamber, each nozzle having its discharge end terminating below ythe throat of its associated secondary Venturi tube and at a point of maximum suction in its mixing chamber for substantially all conditions sof engine operation, an air valve for controlling atlmission of'air to said mixing chambers, `piston and cylinder means for opening said valve, a connectionbetween said cylinder and the throats of v said secondary Venturi tubes whereby said air valve is opened by the mean of the auctions existing in said mixingchambers lat low engine speed and by the mean ofthe increased suctions-pro-r duced by the multiplying action of said secondary Venturi tubes at high engine speeds, and spring means for closing said valve.

17.V In a Vcarburetor of the Lclass described, the combination of a body providing a mixing cham-` ber, an air inlet`therefor vand a cylinder, anozzle discharging into said mixing chamber, a valve Afor said air inlet, apiston inl said cylinder conf` nected to said valve, means vfor operating said piston and air valve, and an air inlet for said cylinder formed in`that part of the body sur-- rounding said first-named inletand comprising two series of alternately overlapping bores -procylinder. 18. In a carburetor of the class described, the

combination of abody'providing a mixing Vcl1an1' b er, an air inlet therefor and a cylinder, a nozzle discharging into saidmlxing chamber, a valve for said air inlet, a piston in said cylinderconcylinder formed in that part of the body surrounding said first-named inlet Vand comprising an arcuate chamber adapted to have an air cleaning medium confined therein.

aoaaar r'. moms. 

